A Lumpy Planet

So you yearn to explore strange worlds in distant galaxies, going where no Earthling has gone before? And you're feeling very depressed that for technical reasons your trip might be delayed a few centuries…or maybe forever? Well, how about visiting the world in this photo? Is it weird enough for you?

Gravity map Courtesy NASA

Surprise! It's Earth. But not as we normally see it. This image shows Earth as it is seen by instruments that are sensitive to gravity instead of light. Gravity isn't the same all over the planet. The mappers turned places where you'd feel slightly heavier into high spots and ones where you'd feel slightly lighter into lows. One of the lows is in India (the blue and pink area to the right of center). You'd weigh about a pound less if you went to India (if you weighed about 100 pounds normally).

Scientists think the gravity map reveals what's going on deep inside Earth, in the part called the mantle, where the rock is still solid but hot enough that it flows slowly. That low off of India may be linked to an ancient collision—the collision of India with Eurasia, which pushed up those wrinkles on the surface of Earth we call the Himalayas.

It just goes to show: There's no place like (or as weird as) home!

Vocabulary

Activity

Scientists believe that an ancient collision of India with Eurasia might be responsible for a lower pull of gravity in that area. What does this indicate about the pull of gravity over time on the planet?[anno: The pull of gravity changes over time.]

What part of the planet do scientists believe is responsible for variations in gravity?[anno: Scientists believe the mantle is responsible for variations in gravity.]

Why might scientists believe that this part of the planet would be responsible for variations in gravity?[anno: Answers will vary but could include that because the mantle is a slow-moving layer of the planet that affects the surface of the planet as it moves, it might also affect the gravitational pull around the surface of the planet.]